The objectives of this study were: (1) to isolate an intestinal spirochete from a nonhuman primate and to characterize it along with several other intestinal spirochetes from a pig, dog, mouse, opossum, and gibbon on the basis of structural and selected biochemical characters, (2) to evaluate these properties using numerical taxonomy in order to provide more information for the classification of such agents, and (3) to further characterize the swine dysentery spirochete (SD).An intestinal spirochete was isolated from a healthy Rhesus monkey and cultivated in vitro under obligate anaerobic conditions on an enriched, fortified blood agar media. Transmission electron microscopy was used to gain some insight into the ultrastructure of this agent. For comparison a number of animal intestinal spirochetes, isolated and available from earlier studies, were studied. These spirochetes were characterized and compared on the basis of several enzymes (API-ZYM('TM)), cellular fatty acids (CFA) analysis (gas chromatography-mass spectrometry), and the data analyzed using computer assisted numerical taxonomy. As part of the study, the swine dysentery spirochete was characterized also by (1) AC heat capacity measurements of its outer cell envelope (OCE) and (2) analysis of certain enzymes and CFA's when cultivated at different temperatures on different growth media.The Rhesus monkey spirochete measured 3.6-4.8 (mu)m x 0.18-0.25 (mu)m and possessed 10 axial fibrils with an OCE sensitive to detergent. It is believed that this is the first report to describe an intestinal spirochete successfully isolated and cultivated from the Rhesus monkey.The presence and absence of key enzymes and CFA's were of value in elucidating the taxonomic interrelationships of these agents. The agents produced distinctive esterase (C4), esterase lipase (C8), and phosphoamidase. The key differential enzymes were alkaline and acid phosphotases, alpha and beta-galactocidases, and alpha and beta-glucosidases. The common CFA's were 3-hydroxydodecanoic, myristic, 12-methyltetradecanoic, 2-hydroxytetradecanoic, palmitic, 14-methylhexadecanoic, and stearic acid.The morphology, biochemistry, and resultant numerical taxonomy suggested that the intestinal spirochetes do not fit into any of the presently defined genera of spirochetes.